Touch-panel-integrated display devices having a touch-panel function are being developed among display devices such as liquid crystal display devices. These touch-panel-integrated display devices can detect a position of contact on a panel surface touched by using an input pen.
Dominant types of input pens used in conventional touch-panel-integrated display devices include resistance-film-type input pens (i.e. a type of input pen in which a position of input is detected by having an upper conductive substrate be in contact with a lower conductive substrate, due to application of pressure) and electrostatic capacity input pens (i.e. a type of input pen in which a position of input is detected by detecting a change in capacitance of a touched location).
In recent years, technology has been progressing which is related to liquid crystal display devices in which photosensitive elements such as photodiodes and phototransistors are provided for each pixel (or for each group of pixels) inside an image display area (e.g., see Patent Literature 1). By embedding photosensitive elements for each pixel in this way, it has become possible to achieve scanner functions and touch-panel functions in standard liquid crystal display devices. In other words, by having the photosensitive elements function as area sensors, it is possible to achieve the touch-panel-integrated liquid crystal display devices.